全文获取类型
收费全文 | 6432篇 |
免费 | 327篇 |
国内免费 | 29篇 |
专业分类
测绘学 | 201篇 |
大气科学 | 461篇 |
地球物理 | 2381篇 |
地质学 | 2224篇 |
海洋学 | 289篇 |
天文学 | 931篇 |
综合类 | 43篇 |
自然地理 | 258篇 |
出版年
2022年 | 60篇 |
2021年 | 134篇 |
2020年 | 126篇 |
2019年 | 106篇 |
2018年 | 291篇 |
2017年 | 265篇 |
2016年 | 411篇 |
2015年 | 305篇 |
2014年 | 324篇 |
2013年 | 414篇 |
2012年 | 353篇 |
2011年 | 315篇 |
2010年 | 284篇 |
2009年 | 321篇 |
2008年 | 239篇 |
2007年 | 182篇 |
2006年 | 171篇 |
2005年 | 138篇 |
2004年 | 137篇 |
2003年 | 137篇 |
2002年 | 111篇 |
2001年 | 103篇 |
2000年 | 101篇 |
1999年 | 63篇 |
1998年 | 90篇 |
1997年 | 77篇 |
1996年 | 49篇 |
1995年 | 74篇 |
1994年 | 84篇 |
1993年 | 51篇 |
1992年 | 50篇 |
1991年 | 44篇 |
1990年 | 61篇 |
1989年 | 45篇 |
1988年 | 42篇 |
1987年 | 40篇 |
1986年 | 44篇 |
1985年 | 50篇 |
1984年 | 39篇 |
1983年 | 48篇 |
1982年 | 54篇 |
1981年 | 42篇 |
1980年 | 45篇 |
1979年 | 44篇 |
1978年 | 52篇 |
1977年 | 44篇 |
1975年 | 41篇 |
1973年 | 44篇 |
1972年 | 33篇 |
1971年 | 40篇 |
排序方式: 共有6788条查询结果,搜索用时 0 毫秒
901.
Yveline Lebreton Josefina Montalbán Jørgen Christensen-Dalsgaard Ian W. Roxburgh Achim Weiss 《Astrophysics and Space Science》2008,316(1-4):187-213
We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT. 相似文献
902.
Brice Ménard Daniel Nestor David Turnshek Anna Quider Gordon Richards Doron Chelouche Sandhya Rao 《Monthly notices of the Royal Astronomical Society》2008,385(2):1053-1066
Using a sample of almost 7000 strong Mg ii absorbers with W 0 > 1 Å and 0.4 < z < 2.2 detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W 0 . We find the amount of dust to increase with cosmic time as τ( z ) ∝ (1 + z )−1.1±0.4 , following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E ( B − V ) and we find that τ∝ ( W 0 )1.9±0.1 , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg ii systems. We measure the upper limit μ < 1.10 and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range 1 < W 0 < 6 Å . We parametrize this effect and provide a correction for recovering the intrinsic ∂ N /∂ W 0 distribution. 相似文献
903.
We report exceptional fireball activity of the Orionid meteor shower in 2006. During four nights in October 2006 the autonomous
fireball observatories of the Czech part of the European Fireball Network (EN) recorded 48 fireballs belonging to the Orionids.
This is significantly more than the total number of Orionids recorded during about five decades long continuous operation
of the EN. Based on precise multi-station photographic and radiometric data we present accurate atmospheric trajectories,
heliocentric orbits, light curves and basic physical properties of 10 Orionid fireballs with atmospheric trajectories that
were long enough and, with one exception, were observed from at least three stations. Seven were recorded in within a 2-h
interval in the night of 20/21 October. Their basic parameters such as radiant positions and heliocentric orbits are very
similar. This high fireball activity originated from a very compact geocentric radiant defined by α = 95.10° ± 0.10° and
δ = 15.50° ± 0.06°. These fireballs most likely belonged to a distinct filament of larger meteoroids trapped in 1:5 resonance
with Jupiter. From detailed light curves and basic fireball classification we found that these meteoroids appertain to the
weakest component of interplanetary matter. 相似文献
904.
Large amounts of particles ejected from the nucleus surface are present in the vicinity of the cometary nuclei when comets
are near the Sun (at heliocentric distances ≤2 AU). The largest dust grains ejected may constitute a hazard for spatial vehicles.
We tried to obtain the bounded orbits of those particles and to investigate their stability along several orbital periods.
The model includes the solar and the cometary gravitational forces and the solar radiation pressure force. The nucleus is
assumed to be spherical. The dust grains are also assumed to be spherical, and radially ejected. We include the effects of
centrifugal forces owing to the comet rotation. An expression for the most heavy particles that can be lifted is proposed.
Using the usual values adopted for the case of Halley’s comet, the largest grains that can be lifted have a diameter about
5 cm, and the term due to the rotation is negligible. However, that term increases the obtained value for the maximum diameter
of the lifted grain in a significant amount when the rotation period is of the order of a few hours. 相似文献
905.
Holtstam Dan Cámara Fernando Skogby Henrik Karlsson Andreas Langhof Jörgen 《Mineralogy and Petrology》2019,113(1):7-16
Mineralogy and Petrology - Potassic-richterite, ideally AKB(NaCa)CMg5TSi8O22W(OH)2, is recognized as a valid member of the amphibole supergroup (IMA-CNMNC 2017–102). Type material is from the... 相似文献
906.
Pinarelli Laura Gioncada Anna Capaccioni Bruno Vaselli Orlando Downes Hilary 《Mineralogy and Petrology》2019,113(1):39-60
Mineralogy and Petrology - Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since... 相似文献
907.
Vizvári Béla Golabi Mahmoud Nedjati Arman Gümüşbuğa Ferhat Izbirak Gokhan 《Natural Hazards》2019,99(1):571-597
Natural Hazards - In this study, a relief system for a large metropolitan city exposed to serious earthquakes is designed and a top-down approach is applied. Afflicted people’s states and... 相似文献
908.
Natural Hazards - This contribution highlights that the paper presented by Ma et al. (Nat Hazards 89(2):741–756, 2017) presents VIF lower than 1 which does not coincide with the natural... 相似文献
909.
Calvetti Francesco di Prisco Claudio Redaelli Irene Sganzerla Anna Vairaktaris Emmanouil 《Acta Geotechnica》2019,14(5):1289-1305
Acta Geotechnica - The evaluation of impact forces exerted by flowing granular masses on rigid obstacles is of fundamental importance for the assessment of the associated risk and for the design of... 相似文献
910.
Lucie Jui
kov Jitka Hor
kov Anna Jansov Jana kodov Tereza Kosov Vojen Loek 《Boreas: An International Journal of Quaternary Research》2019,48(4):929-939
Prehistoric settlements are usually perceived as being in opposition to the natural development of the landscape. Indeed, for woodland snail assemblages in anthropogenic landscapes in central Europe, considerable impoverishment is typical. However, it remains unclear whether this has been caused by humans only or also by climate effects. From an archaeological point of view, the Moravian Karst is one of the classic prehistorical locations in central Europe, but with a more humid climate than the previously studied anthropogenic areas. To learn more about coexistence of humans and natural forests during the Lateglacial and Holocene, we analysed 11 mollusc successions covering this entire area, a unique data set for such a relatively small area. These mollusc successions show several specific features compared to the standard development known from other mid‐European areas. One is that although the Moravian Karst is not far from the Western Carpathians, Carpathian species appeared relatively late, only during the second half of the Holocene climatic optimum. Similarly, some western European and Alpine elements appeared later than expected. In contrast to this, however, a number of forest species with central European range appeared relatively early during the Lateglacial or Early Holocene. Two even survived the Last Glacial Maximum in the Moravian Karst. This would suggest an early occurrence of forest patches in a mosaic landscape. Humans have apparently inhabited this area since the Lateglacial amongst islands of forests, which later changed during the Boreal and then the climatic optimum into humid canopy forests. Thus, a mosaic of anthropogenic and natural habitats persisting in close vicinity was possible in rugged and humid landscapes practically until the Industrial Revolution. 相似文献